Adding tee on feed pipe to drain system

phloaw

Hi, I have a two-pipe fully pumped S plan open vented system.

When I drained it last time, I had the impression there is some sludge or dirt around it. I therefore am going to drain it again to install a magnetic filter.

I was thinking of taking this chance to add a tee on the feed pipe (the one going from F&E tank in the loft to the boiler), immediately before the boiler, to avoid draining it through the boiler in the future, which I'm wary of.

This would be an addition to the traditional draining valve, which I already have after the pump.

Would that make sense at all? Would that be potentially unsafe?

Thanks!