I got sick of carrying water to. That’s what led me to buying longer hoses and using my pumps to transfer water. My regular res pump worked great because I only had about 10-12 feet to move the water. I’ve also seen others buy separate pumps just for water transfer if they had longer distances.
My setup uses an RO unit to fill a 55 gallon cistern. To swap a res, I use a 330 GPH transfer pump to fill a Rubbermaid Brute trash can with 29 gals of RO water. As I drop in each nute, I pump in a little more water to mix the solution. Once the nutes are done, I switch the inlet hose from the cistern to the res and the outlet hose goes out the back door of the garage to a grassy area with trees. The res is 35 gals with 29 gals of nutes. The transfer pump does 5 gals a minute so it only takes 5-6 minutes to empty the res. Then I swap the hoses around - inlet in the trash can, outlet in the res and, in about 5 minutes, the res is ready.
Hoses and pumps - no question. The hoses are the "soft flex" 25' hoses and a 10' has the drain piece for the transfer pump. I was using a 25 gallon tote for nutes but the 32 gallon trash can allows me to refill the res and have about 4-5 gallons that I use over the course of the next week or two. I do res changes about every 10 days - 4 auto flowers in 29 gals of nutes just doesn't make sense to dump out nutes every week.
Water temp is at a steady 68° F - that's the optimal temp for oxygen uptake. After a res change, it take the chiller a couple of hours to drop the temp of the res so I use Hyrdoguard just to be safe.
My grow is in an unheated garage with no drain so I'm really careful with the pumps and also with water+electricity. I make sure to never touch the pump or a power cord while anything is running. The pump runs off a port in a smart switch so I control the pump from my iPhone. I never leave the garage when a pump is running.