unless theres a developer that wont cause my landlord to start asking who's using drain cleaner again/isnt that harmfull to put down a drain.
There's a long debate hiding underneath this seemingly simple remark, which ultimately boils down to the observation that chucking used print developer down the drain is as good or as bad as you subjectively want to believe it to be. Unless your landlord has explicitly made an issue out of your darkroom practice before, I wouldn't bother about it too much. From a technical viewpoint, the comparison between developer and drain cleaner isn't a very fortunate one. A more meaningful comparison would be with the jug of water with a spoonful of sodium carbonate dissolved in it that you used to soak that nasty ingrown toenail or the finger with the infecting splinter in it.
Having said that, there's nothing wrong with avoiding discarding chemistry unnecessarily - quite the opposite. Then again, this might drag us into the discussion at what point it's 'necessary' to discard used developer.
Setting the philosophical aspects aside for a bit, there are three practical routes that come to mind that you might want to pursue.
The first is to use an 'eco-friendly' developer. This is of course relative, since a developer isn't really something you'd feed to your pet goldfish anyway (not even the 'eco' stuff), but at least in some developers, the hydroquinone is replaced by ascorbate, and we may hope/assume that borates are left out of the formulation altogether. I'm not exactly sure how effectively this reduces things like the BOD (biochemical oxygen demand) and the nastiness of borates in wastewater is also debatable, but at least you'll be chucking something labeled "eco" down the drain. Maybe it even comes with a label with the text printed in green. Green is good, we all know this. I'm sorry, I'm not up to date which print developers easily available in the US/NYC come with green print on the label. In the EU, I know that Bellini, Adox and Moersch have 'eco' print developers. (Note that 'eco' might also stand for 'economy'...in which case you'll just have to be optimistic about the whole thing and re-interpret it for your own purposes. Nobody knows for sure, anyway. It just says 'eco'. Make of that what you will.)
The second approach is obviously to skip the drain and save up your used chemistry, and take it away to a facility that's set up to responsibly dispose of it. You mention developer, specifically, but from an environmental viewpoint, the used fixer is more of a concern due to the dissolved silver complexes. So if the landlord's worry is about the eco aspect, then I assume you've already decided that the used fixer needs to be saved up and disposed of responsibly, and you could just as well apply the same routine to the developer. If you want, you can put the used developer and fixer (it's OK to mix them, but preferably do it outside or at least in a well-ventilated area) in an open vessel in a dry spot outdoors (balcony?) shielded from rain so it can evaporate down to a smaller volume. If you print (very) infrequently, the evaporation rate may be sufficient to save you a couple of trips to the waste disposal facility.
The third approach is to try and limit the disposal of used developer by running a replenished system. This is what I personally do, for reasons of laziness (can't be bothered to mix new developer concentrate too often) and economy (why use more stuff than needed, anyway). I keep around a half liter glass bottle of working stock ID62 (you can find the formula here:
http://www.lostlabours.co.uk/photography/formulae/developers/devID62.htm) and another bottle of the concentrate. After a session, I top up the working stock bottle with fresh developer made from concentrate + water. By developing prints in a flat-bottomed tray, I reduce the total volume of developer needed in the first place, so half a liter is more than enough to give me my puny little 8x10's. Scale up as you desire, and/or use a drum if you want to go for optimal economy. A slot processor is also a nice touch, but can be a tad expensive.
A fourth option I'll evidently not recommend, or even mention, is to just ignore whatever you think your landlord has to say about all this and do as you merry well please. Your location says NYC; I don't think the gallon of used, dilute developer you're going to put down the drain every month or so is going to make a whole lot of difference in terms of the conditions of your drains (in fact, the impact is ZERO in this regard) or of the local landscape, environment and biodiversity, which in a metropole like NYC are pretty well screwed anyway. There's no authority that's even capable of tracking down the massive torrent of pollution you're sending down the city sewers for reasons of "can't be bothered", "got bigger fish to fry", "we're happy if stuff torrents in the first place" and "call that a torrent? that ain't as much as a tiny little drop -watcha talkin' about!"
