depending on the filtration you can use the filter to remove the waste, on a canister you use the inlet as a vacuum cleaner, on an internal filter you remove the internal sponges to allow full flow then put a filter sock over the outlet to catch the debris, even just cleaning the filter media (mainly sponge and any filter floss) will be enough to remove a lot of the debris.
also you can get tank vacuums that use the air pump to remove waste.
to do a full tank clean remove any ornaments etc.. and place in a bucket/container with old tank water, remove axolotl and place in tub with clean dechlorinated water, place filter in a container with old tank water, empty syphon water out, clean with bicarbonate of soda/white vinegar/hydrogen peroxide, flush tank out and refill with water adding required amount of dechlorinater and any salts/minerals, then leave for a few hours to make sure all the water is dechlorinated, place ornaments in tank then fit filter (remember to clean filter media in old tank water before refit) and once everything is on and working put axolotl back in, may be worthwhile using bottled bacteria to make up for any lost.
