Sorry - Pump out tank question

[Boatingbiker]

Without wanting to engage in the pump out v cassette debate , I have a question regarding pump out holding tank and vents?.

 

When our holding tank is approx half full and we move across the boat we can hear what appears to be air bubbling up from within the tank. This does not happen when the tank has been emptied nor when three quarters full. This make us think that there is a tank vent somewhere that may be blocked ? Would / could this be one of the holes in the side of the hull near the basin outlet (basin is located above tank)

 

Are holding tanks normally vent to outside ?

 

should I try and probe these holes and unblock it, if one is a vent with a stiff length of wire or a blast of water from the flushing water supply ?

 

Any practical advise welcome, many thanks

[magnetman]

Is it a dump through type? The sort where the toilet bowl sits directly above the tank.

 

I have not had one of these but I think they are usually fitted with a pumpout fitting and a separate vent beside that so probing the vent with a bamboo or metal rod or something may be worthile.

 

I would expect a blocked vent to cause a smell problem indoors in a dump through system.

[Boatingbiker]

yes, it is a dump though system, smells no worst since hearing the air bubbling !

[Iain_S]

If the vent is blocked, there will be a very distinct smell when the dump through is operated. If a blocked vent is causing the bubbling sound, then I'd expect the sound to be very localised, coming from the vent pipework itself.

 

At least bubbling indicates that some decomposition, digestion, etc. is going on!

[Boatingbiker]

thanks for replies received