That's actually a good point about the pee container ttex. I've managed to do the same a couple of times. With a Nature's
Head, the liquids remain contained, but it a bit of a mess
cleaning it all out. Certainly inspires one to keep an eye on the levels, and dump early -- especially if the beers are going to flow

.
Jen&Terry offer excellent
advice. I've only had a fly infestation a few times over the past decade of use, but it isn't fun. It's always been operator-error on my part, when I over-extended the time between emptying, and let the moisture get too high. Having a supply of diatomaceious earth on hand is a good suggestion.
And I too tend to under-fill the bin initially, and then slowly add more as needed. For me that means using roughly 1/2 the coir brick (decompressed) to start, and then after a week or so, start adding handfuls as need be. For two adults, full-time, we tend to get about a month out of each cycle (3-5 weeks).