Submersible Pump

Having spent a lot of time doing water changes on multiple tanks, and spilling a lot of water on both myself and the carpet, the 10L containers I use (segregated/labelled for waste or clean water) are these:-
https://www.amazon.co.uk/h32-Litre-Plastic-Container-Approved/dp/B00TFVJM36/ref=sr_1_2?ie=UTF8&qid=1531037940&sr=8-2&keywords=10+litre+plastic+container
They are slightly larger than 10L, so for the clean water containers I measures out 10L into the container & marked the side to make it easier to add the appropriate amount of dechlorinator.
As for refilling the tank with a submersible pump, this is similar to what I do with my largest tanks, using the external filter, which has a port for this sort of thing. It makes water changes so much easier.
I guess if you get a large plastic stack box to hold the pump that could work. It doesn't have to be large enough to hold all of the clean water as you can add to the container while the pump is working.
The only thing I would point out is get a pump that is strong enough to pump the water to the top of the tank, and not so strong as to blow all of your fish out of the tank. 
I'm using a pump (that can be used submersed or dry) to power the manifold in my river tank, so all I can say is that you really don't want one that powerful -  https://www.amazon.co.uk/Jebao-Jecod-DCT-12000-Speed-12000/dp/B00SWUWV5C but they do smaller ones, as do other manufacturers.

I use a 12-ish litre builder's bucket from B & Q to take the water out. I use a 10 litre bucket from the diy section of a local shop which is graduated on the inside in litres for the new water. The reason I have 2 different buckets is that my husband is obsessed with fish tanks being full of bacteria (should never have used that word  ) so I can't put a dirty, germ ridden bucket into the kitchen sink 

A good place to get food safe containers is a brewing supplier. Im lucky enough to live in an area where home brewing is quite popular (no idea why) so there's a small independent hardware store that has a good selection of home brewing equipment so i was able to get an in and a different shaped out bucket.

Or you could get a connector for your tap and a length of garden hose and fill the tank directly?

If I did that, I wouldn't be able to add de-chlorinator or know how much to use.  Nice idea though

Hoselock tap connectors are what I use to attach the hose to the tap... sorry I couldn't remember the name when I posted yesterday!...