I have to drain my open vented ch system, I have had X400 circulating for a month to try and desludge it. there is what I would call a 'proper' drain tap above the boiler which you can fit a hosepipe to. I presume I can drain the upper part of the system from this tap. However there is no such tap on the lower part of the system, instead there is only the small drain taps fitted to all the ground floor rads. I had to drain a bucket full out before putting in the X400 and it took ages as the water just trickles out. There is a screw nut on these taps. do they come right off? Do I just drain from 1 tap or will I have to go round them all in turn? Looks like it may take a while. How much water approx would the system hold excluding the expansion tank. It is a 3 bed house with 6 rads downstairs (one a double) and 5 upstairs. Any advice welcome.