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Old 21-10-2013, 14:30   #1
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Holding tank: best location for hose in PVC plumbing

I'm installing a new holding tank system, using mostly Sched 40 PVC pipe. For the boat flexing etc, I bought some Trident SaniShield 102 hose. Based on forum topics, Nigel Calder's book, Head Mistress, etc, I've designed a gravity drain system w/ pumpout and decent vent. See attached jpg (not all to scale, but hopefully shows my plan adequately - maybe helpful to others?). It fits in a wooden locker just forward of the head, above the non-heeled waterline on my Seidelmann 37.

I understand that, even with the "best" hose, it is good to use pvc pipe where effluent will stand. Thus the pvc ball valve attached directly to the bottom of the tank, above the seacock - attached to the Trident hose.

For the plumbing fitting that attaches to my Jabsco head outlet, which houses the joker valve, I may be able to find a replacement that will attach to a pvc pipe (instead of a flexible hose w/ clamp). But. I only have about 1-1.5' between head and the planned 90degree pvc elbow to route effluent up to the holding tank (a roughly 2.5-3' vertical distance - don't have exact measurement and am not on boat right now).

QUESTION: So, I wonder if I shouldn't stick with my original plan, with a very short Trident hose attached to the vertical pvc pipe going into the tank. Or, should I put the flexible hose on the vertical part of the system, trying to find some fitting to directly attach pvc to my head? (Not concerned about pvc-local-inflexibility when replacing joker valve etc, as I generally need to pull the pump off anyway given the current configuration of where the head sits).

My original thinking was that the last bit of head pumping will be "clean" water that sits along the short horizontal Trident hose, w/o much mixing of any effluent that didn't quite make it all the way into the tank. Or is it truly best to have the vertical part of the input as the flexible hose (where it may possibly not really just sit)? Just hard to figure where effluent may really end up, especially if I want to flush a minimum of "good" water into the tank to flush the line.

Thanks in advance!
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Old 21-10-2013, 14:53   #2
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Re: Holding tank: best location for hose in PVC plumbing

I'd stick with hose. I have a gravity system; it's been terrific and foolproof after a year with four people onboard full time cruising.

I wouldn't over think it too much, and really another aspect to consider is that you'll probably be replacing your hoses every so often. It depends on usage patterns, how much you flush, the salinity of the water, and other variables. But regardless you'll be changing hoses eventually.

It could also be because of the joker valve, in which case you'll be separating the standing vertical hose from the head (that connects to the holding tank). So that's a great time to switch out hoses as well. Carrying a spare loop of 20' of 1.5" hose isn't so hard or heavy and you can use it for a variety of repairs.

The only other things I'd add:

- It's the not the end of the world but if your vent(s) are to one side, like to port as mine are, a port tack will pressurize the tank a bit and the head stinks. It *shouldn't* be a problem in a properly sealed environment, but there you go.

- Try to put the inspection port directly over the exhaust outlet on the bottom of the tank. If you need to pop it open you can jam a coat hanger straight thru and wiggle it to clear a block.

- I think the PVC ball valve at the bottom of the tank is conceptually a good idea, but adds unneeded plumbing and complexity with little return. The nice thing about a holding tank higher than the waterline is the simplicity of the system.
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Old 21-10-2013, 15:33   #3
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Re: Holding tank: best location for hose in PVC plumbing

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Originally Posted by rebel heart View Post
I'd stick with hose. I have a gravity system; it's been terrific and foolproof after a year with four people onboard full time cruising.

I wouldn't over think it too much, ......
Thanks very much for sharing your experience and recommendations. The overthinking is what I'm probably doing . Unless I hear strong/supported opinions from others, I'll probably go with flexible hose from the head, then to the vertical pvc pipe into the tank. It'll be easy to replace the ca. 1' hose with spare that I have.

Assuming that I can do a good job in supporting the pvc system (aka, keeping the pvc pipe from trying to bend away from tank), staying with mostly pvc seems like a good plan for my particular possible-configuration.

Just want something simple, no-stink, and as easy to maintain as I can. I've already bought the threaded pvc fittings for the tank, along with plenty of pipe. Very inexpensive, even with the $11 pvc ball valve at bottom of the tank. If, years from now, that gravity drain hose needed replacement, it would involve locker dis-assembly and other pains associated w/ pulling the tank. So, I'll stick with the additional valve complexity to be "odor-safe". (I fully understand and appreciate your advice to keep it simple though).

(Just FYI regarding one of your thoughts - the access hatch I showed in my picture isn't a tank port, just a wood door that happens to allow me to see the tank level - another bonus of serendipity w/ my boat's original layout; I ordered my holding tank only with pipe fittings, no access port. I can stick something up the outflow while snorkling below, hopefully keeping away from most of the nasties that could gush out....)

By the way: as I believe the "Head Mistress" has indicated, the Ronco tank I received is very thick and high quality - and they put the fittings wherever I needed them, were nice to work with.
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Old 21-10-2013, 15:51   #4
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Re: Holding tank: best location for hose in PVC plumbing

FWIW: You can simplify your system by putting a Tee in the hose below the tank (between the seacock and bottom tank outlet) and use that for pumpout... you'll get a complete pumpout also.
Not sure I'd want an access hatch on the side.... sounds like a smelly leak waiting to happen... even minimal seepage will smell.
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Old 21-10-2013, 16:01   #5
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Re: Holding tank: best location for hose in PVC plumbing

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Originally Posted by Cheechako View Post
FWIW: You can simplify your system by putting a Tee in the hose below the tank ....
Yow. Thank you. I really wish I'd thought of that - excellent. Also saves me from doing smaller-diameter pumpout pipe to go down from the top of the tank. Ah well, a simple cap on the existing 1.5" fitting on top is easy, and that small "port" could (remote chance) allow some kind of usefull access in future problem.

You folks are great!
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Old 21-10-2013, 16:05   #6
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Re: Holding tank: best location for hose in PVC plumbing

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Originally Posted by Cheechako View Post
... Not sure I'd want an access hatch on the side.....
Just FYI: My diagram wasn't clear on the access hatch. There's no port into the tank, that note on access was only a wood door into the wood locker containing the tank (there are only 4 pipe fittings in the tank - now effectively 3 thanks to your suggestion!).
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Old 21-10-2013, 17:24   #7
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Re: Holding tank: best location for hose in PVC plumbing

Sounds great! I used the Tee with the gravity drain on one boat, it pumped very clean and drained while motoring too.
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Old 21-10-2013, 17:47   #8
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Re: Holding tank: best location for hose in PVC plumbing

Ditto RebelHeart and Cheechako. But, if you add a second large vent line, aim them port and starboard, you can then use aerobic bacteria such as "K.O." and be done with the bad smells. Here's mine. You can see the tee that Cheechako refers to:
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Old 21-10-2013, 17:52   #9
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Re: Holding tank: best location for hose in PVC plumbing

Don't put the white PVC valves in there......I'm replacing mine after 3 years, the ball seized and I twisted the shaft off. I'm considering marelon next, or bronze.
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Old 21-10-2013, 18:25   #10
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Re: Holding tank: best location for hose in PVC plumbing

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Don't put the white PVC valves in there.....
Ouch. Your bad experience w/ those valves is another example of type of info I'm interested in. I saw the "white PVC valve" at Home Depot, but didn't like their friction. Lowes had similar, but just "felt" right in operation (with no obvious lubrication) - so I bought the PVC valve at Lowes.

Given how this is not a critical valve (seacock always closed unless dumping well-offshore), I'm reluctant to do Marelon etc for valve. (But did get a Marelon 1.5" thread-to-hose barb fitting, perhaps mainly cause I was at West and had had a hard time finding item at hardware stores .

Not to sound rude - but did you use/turn your valve very often during the 3 years prior to failure? Rather than buying a thru-hull seacock quality valve, I may just resolve to pull my tank and replace the valve every few years.

Any further thoughts on this from your experience? Thanks again for your input.
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Old 21-10-2013, 18:31   #11
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Quote:
Originally Posted by ephyraboater View Post
Ouch. Your bad experience w/ those valves is another example of type of info I'm interested in. I saw the "white PVC valve" at Home Depot, but didn't like their friction. Lowes had similar, but just "felt" right in operation (with no obvious lubrication) - so I bought the PVC valve at Lowes. Given how this is not a critical valve (seacock always closed unless dumping well-offshore), I'm reluctant to do Marelon etc for valve. (But did get a Marelon 1.5" thread-to-hose barb fitting, perhaps mainly cause I was at West and had had a hard time finding item at hardware stores . Not to sound rude - but did you use/turn your valve very often during the 3 years prior to failure? Rather than buying a thru-hull seacock quality valve, I may just resolve to pull my tank and replace the valve every few years. Any further thoughts on this from your experience? Thanks again for your input.
The valve was actuated, in the first year once a month or so, then the following year daily while cruising, followed by a return to the once a month schedule. During this time it became progressively more difficult to operate and was squeaking whenever turned.
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Old 21-10-2013, 18:47   #12
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Re: Holding tank: best location for hose in PVC plumbing

I would not bevel the dip tube, as the fluid level will not be drawn off lower then the top of the bevel. Better to have a flat inlet with inlet about 1/2 3/4 above bottom of the tank.
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Old 21-10-2013, 19:12   #13
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Re: Holding tank: best location for hose in PVC plumbing

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The valve was actuated, in the first year once a month or so, then the following year daily while cruising, followed by a return to the once a month schedule. During this time it became progressively more difficult to operate and was squeaking whenever turned.
Very good to know - thanks again. Perhaps these hardware store valves aren't up to the task we're discussing. That makes me very inclined to simplify (per Rebel Heart's early suggestion) and go w/o a valve attached to tank. (This is contrary to what I remember from info from the "Head Mistress" and Nigel Calder etc regarding hose smell permeation, but, maybe this is easiest in long run, w/o very expensive valve?)

So, for ("new") topic of tank bottom outflow: Simple pvc Tee-fitting from tank bottom, with T going to PVC pipe (and eventual flexible hose) for pumpout, and straight part of T connected to (hi-quality Trident SaniShield 102) flex hose to seacock.

Anyone disagree? How about related, original question on effluent sitting in short horizontal hose from head, then up ca. 3' of PVC, vs hose on vertical route?

Again - wonderful to get this great input! Awesome.
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Old 21-10-2013, 19:33   #14
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Re: Holding tank: best location for hose in PVC plumbing

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I would not bevel the dip tube, as the fluid level will not be drawn off lower then the top of the bevel. Better to have a flat inlet with inlet about 1/2 3/4 above bottom of the tank.
Good point re my diagram - showed way too much bevel, just one of the inaccuracies in it. This was originally a rough diagram to help me plan - tried to correct things for posting here, but ....

More to the point, it seems best to have no bevel as you said. But in the interim of postings, it was pointed out I can use the bottom outflow (Tee'd) for pumpout in addition to gravity dump. So I'm nixing the top-mounted pumpout complexity.

Thanks. And it sounds like, when I'm done, maybe I should post an updated diagram that's more accurate, maybe helping others in similar designs(?). Of course, that would assume all works well......
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Old 21-10-2013, 19:47   #15
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Re: Holding tank: best location for hose in PVC plumbing

If you can do it don't make the tank a rectangle. Slope the bottom of the tank so that the drain is always at the bottom of the tank so that it always completely drains. I also agree with the "T" in the drain for the pump out.
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