I just drained down the heating system in my house (used protector after adding 3 rads a few weeks ago so now adding inhibitor). It's straightforward because there are lots of rads with drain taps on. But I did find I was having to go from rad to rad draining down to get it all out... presumably if there is only one drain tap then it must be very hard to empty a system? Do plumbers just get what they can out and accepts some is still in there? Do they suck it out with anything?