We have never had a problem. I do always try to lift the anchor from the fo’c’sle and, if the chain is too muddy, I dunk it back in the water to rinse it off. I can also pick off any big bits of weed that come up but we never wash it. We do sail the south coast of the UK and so the weather is not too hot, but we have never had any smells from the locker. David.
We have a chain brush that wraps around chain and “scrubs” it while being hauled up. We use a boat hook to hold the brush just below the waterline while the windlass hauls. This gets off small bits. BTW – this chain brush is made by Davis but I think it’s a discontinued product. I’ve never seen another one like it either. Ours came with the boat, and when it breaks we repair it. Handle thing indeed!
Back to hauling up the anchor – larger seaweed bits that make it up to deck level get picked by hand (with the windlass stopped).
The muddiest bit (like the anchor) gets hand dunked multiple times.
Depending on the anchorage bottom, the chain can be smelly for a day, but it gets a nice bath at the next anchorage. I don’t find it to be a problem. We don’t anchor in muddy bottoms much.
Our anchor locker is in the forward-most bow section, not the original locker further aft that has the chain fall through the berth cushions. This is both good and bad. The good is that the chain doesn’t sneak between the cushions. The bad is that there is more weight further forward and higher (not ideal for boat trim) and the slope of the bow is not enough for the chain to always fall nicely (sometimes it needs a tug from below – hassle!).