Opportunity is missed by most people because it is dressed in overalls and looks like work. - Thomas Edison
about once every 6 months to 9 months. You can get some neutralizer from either easiway or franmar and dump it down the drain. The sludge at the bottom should be cured in the oven before disposal. It's usually a sheet of old emulsion and ink.
We've only been using ours for maybe 4-6 months or so but it's still going strong. We have the big, white polypropylene Blackline tank. Franmar One Step but we remove ink before putting the screens in to strip the emulsion. I don't know why everyone else can use this stuff to remove both ink and emulsion but we sure as hell can't get away with that. Could be the phthalate-free thing. I think the main thing is to pull the screens before the emulsion sloughs off and disperses in the tank. That and something to hang the screens up over the tank to drip back in- or use a squeegee to conserve solution. The more times you have to top it off with water, the weaker it gets.
I am pretty sure you can add a tap. I will have to try that when I drain this thing. The one thing I dont like about a dip tank is that it warps the wooden frames but I guess thats to be expected.