All of my darkrooms have been in basements or attic storerooms where heat, water, floor joists, and sewer pipes have been running through, thus allowing for multiple sites where light can get in. I've discovered over the years, that absolute light-tightness is not necessary. The trick is getting it to be light-tight where needed and then not worrying about the rest. For 4X5 tray developing, which is the only kind I do, I always have the developing trays in the sink (which has a six-inch side), so the film and trays are blocked from any light leaks coming under or around the door by the sides of the sink. If the light leaks are down low, there's little to worry about. If they're above sink level and overlooking the sink, then they need attention. I've discovered that black felt, wall joint compound, and flat black paint are wonderful things. Wherever I've got a leak that can't be 100% sealed off because of weird-shaped openings or pipes, etc., I paint around it with flat black paint which, if the leak is a very small one, is often sufficient to neutralize it. The only fogging problem I've ever had due to extraneous light came from developing my sheet film beneath a too-bright Gralab timer, which I now cover with a cloth.
Larry
Two things