Reef

BFOK

What line are you using? Some materials like Spectra lose a lot of strength if knotted in too tight a radius.

Galvanised steel core plastic all weather. Didn't go for rope as it's so damp here I thought it would go green during wet periods

Tumble dryer.

Double-fisherman's

or just figure-of-8

It's  getting tied to fixed anchor hooks not joining with the opposite end or another line.

Round turn and 2 half hitches for me !

Bowling on the fixed end, taught line hitch on the other...

As it's essentially wire rope, perhaps consider some of those appropriately sized wire rope clamps. Pull taut at the other end and tighten that clamp. Then add an extra clamp at each end for those heavier wet items.

cant tie knots? just tie lots!

Has served me well, although the instructor on my rope rescue course disagreed with that moto, pfffft what does he know.

I use a figure of 8 and a trucker's dolly knot

I use the little clamps and a galvanised ferrule/eyelet to make to turn smooth.

Otherwise round turn and two half hitches or anchor hitch/fisherman's bend.

I'd use either a Horsetail half flange spigot knot or a series of four granny knots.

clamps and a galvanised ferrule/eyelet to make to turn smooth

This.

(If you are going to ask advice online about how to put up a ****ing washing line, you might as well end up doing the job properly 👍😂)

Well they stretch a lot being basically cables, so I would tie an initial knot with a view to having to re tie it a few times until it settled down a bit.

Stokers dhoby hitch.