Header Tank Vent Pipe Size

[ianc1200]

I bought a boat which has two header tanks (one for forward heads, one for aft), however the toilets are not connected to these tanks and discharge to sea directly via the seacocks. The old pipework is there, including diverter valves, 1 1/2" emptying pipes to a deck fitting, several "Y" connecters, Whale pumps so the tank can be discharged via the seacocks etc. We would like to go to the upper Thames, Broads etc, using the tanks & pump out facilties, so have been looking at plumbing layouts, having found the Tek-Tanks website very useful. However ther tanks we have fitted have a 3/4" dia vent to outside the hull, just as many fuel tanks have. The Tek-Tanks information shows 1 1/2" vent pipes. Is it likely we'll have problems using the existing 3/4" vent pipes?

 

[PaulRainbow]

I bought a boat which has two header tanks (one for forward heads, one for aft), however the toilets are not connected to these tanks and discharge to sea directly via the seacocks. The old pipework is there, including diverter valves, 1 1/2" emptying pipes to a deck fitting, several "Y" connecters, Whale pumps so the tank can be discharged via the seacocks etc. We would like to go to the upper Thames, Broads etc, using the tanks & pump out facilties, so have been looking at plumbing layouts, having found the Tek-Tanks website very useful. However ther tanks we have fitted have a 3/4" dia vent to outside the hull, just as many fuel tanks have. The Tek-Tanks information shows 1 1/2" vent pipes. Is it likely we'll have problems using the existing 3/4" vent pipes?

When yo say header tanks, do you mean holding tanks ?

We have Tek-Tanks for freshwater, 1 1/2" fill hose and 3/4" vent. We can fill the tanks as fast as the marina water suppy is capable of, with no problems. So, perhaps you'll be OK Ian.

 

[snowbird30ds]

It would depend on how hard the pumpouts suck.

 

[TiggerToo]

It would depend on how hard the pumpouts suck.

Yes, agree.

I would also suggest you contact TekTanks. They have been very good at talking to me about the installation I am about to set up.

 

[ianc1200]

Yes, apologies I meant holding tanks (for toilets). Retro fitting larger dia vent pipes into existing old tanks fills me with dread - I thinking new tanks/pipes/pumps etc are needed. Thanks for thoughts/comments.

 

[BobnLesley]

... I meant holding tanks (for toilets). Retro fitting larger dia vent pipes into existing old tanks fills me with dread...

I installed our holding tank using 1.5" hoses all round, just like everyone else in the UK/Europe seemed to be advised to do.
However, when we reached the Caribbean I noticed that breather hoses on the overwhelming majority of North American boats I saw were only 3/4". As a generalisation, those North American boats are more often subject to vacuum pump outs (I believe a deck pump-out point is nowadays a required fitting on US boats) yet I never saw or heard of anyone suffering tank collapse problems (which is what I was warned of) due to these restricted breather pipes.
If I were ever to install a new holding tank, I would use a smaller/tidier 3/4" breather pipe.