When the tanks start getting big even Pythons can be daunting. I don't like the idea of wasting "clean" water to suck out the dirty, and forget possibly getting some substrate down the sink and clogging it up. Even with strainers I done cost us at least $400 worth of drain cloggers and plumbers visits by sucking sand into the sink.
Doing several hundred gallons worth of waterchanges weekly we've found 3 pieces of equipment essential.
1.
pump
2. length of 1"
vinyl tubing (we use 25 & 50ft lengths)
3. a
garden hose
Connecting the tubing to the pump we get the water out of the tank. Our trees really seem to like the big waterings of tank waste

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Why not just use gravity? Lots of our tanks are in the basement. The water has to go UP to get out. After the old water's out the new water needs to come in. We have garden hoses connected to outdoor faucets that get both hot and cold water so it's not a pain in the ass to get the temp right. Refill the tanks. I add conditioner to each tank a little at a time.
I don't wait till it fills up and then add the conditioner, I've killed fish that way.
I don't add all the needed conditioner and then add the new water, I've killed fish that way.
With a little conditioner at a time the fish don't even get irritated. Rubbing, flicking, twitching and panicked swimming are what the fish do with they are irritated by the chemicals in the new water.
Here, after the addition of chloramine (which they added to the water quite a bit before they let everyone know in the city's water report), small-medium fish die very quickly. Slow and painful for the larger fish. You can't age or aerate chloramine out of the water like you can chlorine and if your water has chloramine you need a conditioner that will neutralize it.
I use Amquel+ cause it's readily available in my area. Other people swear up and down by Prime and snottily look down opon anything else but whatever you can find, as long as it neutralizes and/or eliminates ammonia, nitrates, chlorine, chloramines and other undesirable additives/metals you're fine. Most of these measure out in teaspoons or tablespoons per 10 gallons. Much easier to figure out than drops

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