I agree with the comment of using a tub to serve as the sump. Any number of small submersible pumps designed for sumps should work. I'd want the tub as large as possible to provide a buffer for the pump.
I'm more concerned about the chemicals you will be putting into the septic system. I'm in the same situation with a darkroom I'll be building in a lake home. It's been hard to find solid information. So for now I plan to dump the chemicals is a 3 to 5 gal container; then basically use the drain for washwater. (Of course, you'll need a place to properly dispose of the chemicals in the container.)
We'll have a gravity system so no pump (yeah!) but minimizing the chemicals would help prolong the life of the pump in your situation.
Well, I will keep looking for the best price possible for a grey water pump - it seems to be a better solution than a sump pump, requiring less water to start pumping than a standard sump.
Meanwhile, I have more clearing to do in the area the darkroom is going in, and possible more to worry about when Hurrican Noel storms by tonight with 120 km/h winds and heavy rain. I may have a little more water than a sinkful to get rid of:rolleyes:
There are two potential interpretations of this. One is that the chemicals could cause damage to the components of the drain - reservoir, pump and piping. My experience, based on using a system like this for more than 25 years, is that there is no problem. The vast majority of the liquid in the system is wash water, and given that level of dilution, the chemicals are simply too dilute to be able to do any harm to the plumbing components.
Originally Posted by mgb74
The other concern is environmental. There has been a lot of discussion about this topic. Most chemicals from residential darkrooms are innocuous, but there could be concern with heavy metal contamination from exhausted fixer. There are a couple of ways of removing the silver in exhausted fixer - the electrolytic process involves a couple of electrodes and a source of dc - perhaps an old "wall wart" dc power supply or battery charger. The other is ion exchange - put the used fixer in a plastic container (I use a plastic box that originally held deck screws), drop in a bit of steel wool, and let it sit for a few days until the steel wood dissolves completely. The iron in the steel wool will displace the silver ions in the fixer, causing the steel wool to gradually dissolve, and the silver will precipitate out as sludge. Decant off the liquid and dump it down the drain - at that point, it is no more harmful than water from a well that contains a high level of iron. Let the sludge dry, and either dispose of it in the garbage, or save it in hopes that the price of silver goes up and it becomes valuable.
The fact that you are thinking about a darkroom at a lake property raises another concern - there could be local regulations about waste disposal that have to do with the proximity to the lake and the potential impact on recreation. The major concern is likely for e-coli and other bacterial contamination. If you take the appropriate steps to address those concerns (which probably means locating the septic system a decent distance from the lake), then you probably won't need to do anything about darkroom waste other than deslivering your used fixer.