Fore to Aft Holding Tank Crossflow

[crquisto]

When I bought my 2000 Carver 406, one of the first things I did was have the holding tanks pumped out. I noted that the forward Tankwatch III was not giving and indications while the aft tank showed empty when pumped out. I decided to used the forward head/tank only with RV Digest-It in an attempt to clean up the switches on the Tankwatch. After a short while, I got a mid-level light on the aft holding tank. The aft head had not been used. After watching this through several pumpouts and opening the forward holding tank, I've determined that my forward tank is likely draining to the aft holding tank by gravity. Having chased down the sanitary hoses, the only way I see for this to be possible is if the y-valve by the overboard discharge pump has failed and is allowing forward to aft flow. Has anyone ever heard of this? Should I just replace the y-valve? It doesn't turn anyway, but I never pump overboard, so I wouldn't need to replace it for that reason. Cost is not an issue - just hoping to avoid the dreaded onboard sewage spill.

[Lyndon670]

That is the only connection between the fore and aft. It must be stuck in the open position allowing the "stuff" to run back. did you try pinching off the hose with large visegrips (with rubber hose on the teeth)? Would be worth a shot to prove your theory.

[crquisto]

Haven't tried that. A little afraid of destroying the hose, but based on what you've said and what I've seen, I guess I'll just replace the y-valve. Thanks, and I'll let you know how it comes out.

[crquisto]

Problem is fixed! I don't know how there was a leak because the y-valve appeared ok, but I rebuilt it anyway and have no more problems with cross flow. I pumped everything out first and had minimal drippage which came from the overboard discharge pump but was easily handled by placing absorbent pads under the working area. Two weeks of use and there is no leakage thru to the aft tank.