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Old 06-12-2016, 20:04   #1
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converting fresh water flush to lake?

My head pulls the flush water from my water tank">fresh water tank. With only 30 gallons it can go quickly. I understand that it's not typically desirable to pull in salt water for ongoing use, but since 99% of my use is on fresh water inland lakes, are there any disadvantages to converting mine to pull from a thru-hull?
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Old 06-12-2016, 20:18   #2
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Re: converting fresh water flush to lake?

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My head pulls the flush water from my fresh water tank. With only 30 gallons it can go quickly. I understand that it's not typically desirable to pull in salt water for ongoing use, but since 99% of my use is on fresh water inland lakes, are there any disadvantages to converting mine to pull from a thru-hull?
a. I hope you have some manner of backflow preventer, because pulling directly from a freshwater tank is a big no-no.

b. Even brackish water, like the upper Chesapeake Bay, causes very few problems. Make the change. Only consistent use of seawater is troublesome. You may get some odors, depending on the specifics, but no important harm.
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Old 06-12-2016, 21:49   #3
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Re: converting fresh water flush to lake?

I've never heard of the use of seawater in heads as to be undssirable, or something which causes problems. It's the norm for every boat I've ever been on. And I'd think that having a head hooked up to one's fresh water system could be quite tricky, with some perilous consequences if done incorrectly.
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Old 06-12-2016, 23:17   #4
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Re: converting fresh water flush to lake?

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I've never heard of the use of seawater in heads as to be undssirable, or something which causes problems. It's the norm for every boat I've ever been on. And I'd think that having a head hooked up to one's fresh water system could be quite tricky, with some perilous consequences if done incorrectly.
Quite common, actually, though more for day sailors than cruisers. I go back and forth, depending on whether freshwater is available.

  1. Less odor. The sulfate in the seawater is a big odor source, both on the intake side and in the holding tank.
  2. Less scaling. Hoses and jokers last longer because there is little calcium (seawater is nearly saturated). Much less scaling.
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Old 07-12-2016, 01:35   #5
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Re: converting fresh water flush to lake?

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Quite common, actually, though more for day sailors than cruisers. I go back and forth, depending on whether freshwater is available.
  1. Less odor. The sulfate in the seawater is a big odor source, both on the intake side and in the holding tank.
  2. Less scaling. Hoses and jokers last longer because there is little calcium (seawater is nearly saturated). Much less scaling.
Salt water smells are an issue for some but no problem if you liveaboard and do lengthy flushes frequently. More of a problem for those who leave salt water in the system for a length of time.
Scaling is from urine/salt water precipitation. Long flushes that clear the pipes of urine is the way most cruisers mitigate this problem.
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Old 07-12-2016, 04:06   #6
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Re: converting fresh water flush to lake?

FWIW, my 30 year old Cal has had salt water flush since day-one. The first head/discharge hoses lasted for 20 of those years, AND the head was only replaced because I wanted to get a manual instead of electric. The secret to longevity is to thoroughly flush fresh water through the system whenever the boat is to be put up for any length of time over a few days.
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Old 07-12-2016, 05:44   #7
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Re: converting fresh water flush to lake?

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... I hope you have some manner of backflow preventer, because pulling directly from a freshwater tank is a big no-no. ...
Please understand the importance of the above. In simple terms: Your potable water may have a direct connection to your marine toilet. Unlike shore side toilets, marine toilets (AKA: heads) typically let flushing water directly into the bowl (no tank w/ air gap). While the typical water flow is directional, conditions may occur in which flow, bacteria, etc. maybe able to go the other way into your drinking water tank. A typical check valve is not sufficient, a back flow preventer is needed.
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Old 07-12-2016, 05:48   #8
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Re: converting fresh water flush to lake?

Thanks guys. I figured in my case the benefits for a lake draw would far outweigh and benefits on the other side, but I wanted to check and make sure I wasn't overlooking something.
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Old 07-12-2016, 09:01   #9
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Re: converting fresh water flush to lake?

Raw water flush has never been a problem for me so I say go for it.


Since your current head expects the water to be pressurized, the simplest and best plan would be to purchase a new head designed for raw water flushing. The low end Jabsco manual head has worked fine for us for years. You will need a thruhull and seacock as well as the head.


For a boat that heels from time to time, you may also need a siphon break. The head comes with instructions.
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Old 07-12-2016, 09:56   #10
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Re: converting fresh water flush to lake?

Before I converted to fresh water flush, both my heads were plumbed into the engines Thru hull, it caused no problems and was manufactured that way. I wouldn't install a separate thru hull for a head
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Old 07-12-2016, 21:26   #11
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Re: converting fresh water flush to lake?

Salt water works fine in a head that's used regularly. The odor issue comes when salt water is allowed to stand in the toilet and hoses for weeks or months. Regularly pump water through the head system and all is fine.

One issue with saltwater is scaling when mixed with urine. After a couple years of constant use both live aboard and cruising the exhaust hose became blocked with a calcium like product. I disconnected the hose and beat the crap out of it to loosen the scaling and reinstalled. It was still working fine when we sold the boat 8 years later though the head had limited use for most of that period. Understand that occasional flushing with vinegar or other mild acid solution will keep the scaling at bay.
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Old 07-12-2016, 22:12   #12
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Re: converting fresh water flush to lake?

VACUFLUSH system is designed for FRESH water flushing, there selling point is a minumun amout of water used to flush, about one pint !, it is indeed designed for FRESH water, not salt, iv'e had one and the system works as advertised.
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Old 08-12-2016, 08:17   #13
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Re: converting fresh water flush to lake?

No one has asked the most important question: is your toilet designed to use onboard pressurized fresh water, or is it a seawater toilet that a PO has connected to the fresh water plumbing?

If it's a toilet designed to use onboard pressurized fresh water, it can be converted to sea water flush, but you'd have to add a remote intake pump to do it because fresh water toilets don't have an intake pump, just a solenoid that opens and closes the fresh water feed to the toilet.

If it's a sea water pump that's been connected to the fresh water plumbing, all the previous replies are spot on...it never should have been. However, because it does have an intake pump, all you should have to do it run the inlet line to a thru-hull.

If you're not sure what you have, What's the make/model age of the toilet?

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Old 08-12-2016, 08:47   #14
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Re: converting fresh water flush to lake?

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No one has asked the most important question: is your toilet designed to use onboard pressurized fresh water, or is it a seawater toilet that a PO has connected to the fresh water plumbing?
I sort of asked that in post #9. I assumed the head was a proper fresh water head because he said his head used fresh water.
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Old 08-12-2016, 11:57   #15
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Re: converting fresh water flush to lake?

Thanks Peggie. I was wondering about this issue, but wasn't sure how to put it into words. All of the previous heads I'm familiar with were manual and pulled from the lake.

This head is on a 1987 Sea Ray and I assume it is original. It's an electric Thetford. I don't know if the electric pump on the head counts for an intake pump or if I'll need to add a pump to get water from the thru-hull to the head.

Photos of the head included here:




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