Ok, so I've got this Stenner pump which is pumping bleach into a spa. The tank has a lip on the top (see picture) surface underneath the pump which accumulates water when it rains, so I sealed the drainage hole from the pump into the tank with caulk.
But when I did that, the tank could not vent any air and tank would bulge until it leaked bleach everywhere out through the cap onto the top surface. To fix that problem, I drilled a small hole in the side of the tank, but I think there might be a lot of bleach evaporating through that hole (it gets easily in to the mid-90's now here in Texas...)
So my question is how can I properly vent the tank without losing much bleach through evaporation? Thanks.