Thanks. I flush with fresh water, so that's not the issue. I've thought about increasing the vent hose size (currently 1/2" i.d.) and running two of them. One issue is how to attach the hose to the tank. There's no access port and I'm reluctant to add one -the fewer holes the better! So I can't put one of these in.
The tank is plastic, so I wouldn't think I could tap threads for one of these:
And it doesn't make sense to me to attach a 1" i.d. hose to a 1/2" opening.
Also, the screened vent to the outside would need to be replaced with something I have yet to find.
Any ideas would be appreciated. TIA