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Old 10-05-2024, 20:01   #1
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Holding Tank Fitting Stress

I just replaced a toilet to holding tank sanitation hose. The hose fits onto a right angle tank fitting which screws into male threads that are fitted to the top of the holding tank.


After installing the hose onto the fitting, I had to bend the hose to permit the threads of the connector to mate with those present on the top of the tank. Although all assembled well and the fitting (with limited testing) seems to be leak free, I am concerned that the hose might be exerting too much force on the tank top connector.

The tank is made of some sort of plastic material and the fitting is also plastic, (? PVC) of some type.

Can this damage the tank? Is there a way to judge if the stress is too great? I'm terrified I might cut the hose too short.
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Old 11-05-2024, 09:00   #2
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Re: Holding Tank Fitting Stress

First we need make sure we're both talking about the same things: Tanks have female threaded fittings into which a PVC (sched. 80 is best) male thread -barb hose fitting is threaded. That fitting can be straight, or a 90 or even 45 degrees, depending where the hose connected to it is coming from or has to go.

Any side-side stress on hose fitting will cause problems even if not any actual damage. Stress to one side or up or down, will cause the connection at the tank to leak and can even crack the female tank fitting. This problem is easy to prevent by using 90 or 45 degree fittings instead of straight (or replacing a 90 with a straight or 45).

If you had to bend the hose to get it onto the tank thread-barb hose fitting, you definitely need to replace that straight fitting with a 90 or 45 degree hose fitting.

Do NOT over-tighten threaded fittings! Tank fittings are NPT standard which is slightly tapered-TOO slightly to be seen by naked in female fittings that short. Over-tightening the male fitting will cause the female "collar" to crack...so tighten male fittings no more than 1/2 turn past hand tight. I like to wrap the threads of the hose fitting with plenty of Teflon tape...I dont recommend using any other sealant. You're welcome to give me a shout via PM if you need more help.

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Old 11-05-2024, 09:23   #3
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Re: Holding Tank Fitting Stress

the hose should be pretty flexible since it is new. but i would say that excessive stress on that plastic fitting could be a problem you don't want to deal with. would a straight fitting be better than the 90 degree at the tank? good luck with it.
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Old 11-05-2024, 14:05   #4
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Re: Holding Tank Fitting Stress

Emphasizing what Peg said, be a bit careful when using teflon tape on plastic fittings. Teflon reduces friction enough that it is very easy to over-tighten the fitting, possibly breaking the female part. Generally, I hand-tighten, then no more that one additional turn to align all.
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Old 11-05-2024, 14:24   #5
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Re: Holding Tank Fitting Stress

The OP plainly stated that there already is a 90 fitting on the tank.
Perhaps a perusal thru some available fittings may solve the issue.
Would add that 22-1/2-degree elbows are available to use with the hose adaptors.

https://marinesan.com/pvc-fittings/
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Old 12-05-2024, 18:32   #6
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Re: Holding Tank Fitting Stress

Thanks to all who took the effort to reply, private message, etc.


My fittings were optimal in configuration. I elected to remove the possible stress on the holding tank fitting and the underlying tank wall, by removing 4 additional inches of new sanitation hose.
The initial sizing of the hose length was made more challenging because I had too much extra hose and it did not fit easily into the holding tank compartment. This made it hard to line the hose up with the fitting and mark it properly for cutting. Initially, my bias was to favor cutting the hose too long for obvious reasons, not understanding the possible significance of this until after it was done.

The fittings were removed by hand with effort but no wrench required when I removed the original hose. I elected to tighten the fittings by hand without using teflon tape when I attached the new hose. The fittings on this boat are sealed with an O-ring. I applied a small amount of silicone grease to these. In the 12 years that I have owned this boat, there has never been a leak at a fitting, so my presumption is that the teflon tape is not necessary. Time will tell. I will monitor everything and can easily add the tape later if it is necessary.
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Old 13-05-2024, 18:39   #7
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Re: Holding Tank Fitting Stress

Best answer possible, congrats
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