In line fuel filter, recommendations

... a filter in the tap which should keep most of the rubbish out. Unfortunately this means removing the tap (hence draining the tank) to clean it. I have used one of these with good effect on a non-Norton:

https://www.classicbikeshop.co.uk/in-line-chrome-fuel-filter.html

Sounds like time to replace petrol pipes. Ethanol proof rubber lines recommended.
The old ones don't like modern "petrol". All fuel lines does become hard with age.
Plastic pipes get hard faster. Find easily bending rubber tubes. Many modern ones are stiffer because they are designed for the higher pressure from fuel pumps and have bigger outside diameter.
The cheap plastic transparent filters works for me. You can see amount of debris. But there are metal filters too, some with transparent middle.
Yesterday bought very small plastic ones intended for lawn movers for a two stroke racer where short total length was needed.
 

Mark, have a look at Apico petrol pipe and fuel filter. The pipe has lasted well on my bikes and they do metal bodied fuel filters. 

I think  ian_soady

Is right I have had them on My Triumph for a few years and never had a problem with them, when need to clean just take them off unscrew clean and put back.

Cheers Mo

which is very flexible and doesn't seem to be damaged by modern fuels.

https://www.carbuilder.com/products/low-pressure-fuel-vent-drain-hose-6mm-2?_pos=1&_sid=fc263323a&_ss=r

Having perused the link above I would be asking the seller if the hose will withstand petrol continuously rather than as the heading says suitable as a "vent and drain" hose.

Hose marked SAEJ30R9 is supposed to be proof against E10 petrol.

Mark, I had the original Norton supplied clear plastic in-line fuel filter in my Commander.
Then ethanol arrived. 
The bores of the inlet and outlet reduced. The inlet and outlet pipes were no longer aligned. 
Bike started to run weak on high throttle. 
And then the pipe 90% fell off the filter output, dropping a large proportion of the fuel tank contents over my right leg and the very hot exhaust system. The engine still coughing along. Stopped in a lay-bye because fuel gauge dropping rapidly.

I consider that one of my 9 lives. 

The plastic had become soft with the ethanol. The tight pipe clips had squished the connectors and were no longer tight. The bores of the connectors were about half their original size. 

I only trust metal bodied filters now. 

Peter
 

Ive been using Pingel fuel filters for years, expensive and in my opinion worth it

Ist doch eigentlich ganz einfach, die Filter im Vergaser reichen völlig aus, also die im Tank entfernen. Es trägt ja auch keiner seine Hose mit Gürtel und Hosenträgern, oder? Wenn Gummischlauch dann innen NBR und außen Neopren, am besten bei BMW kaufen, halten ewig. Ich bevorzuge beim Antichrist (Norton Commando) durchsichtige Schläuche aus Polyurethan bleiben auch bei ethanolhaltigem Sprit durchsichtig und elastisch. Und vor allem MUSS die schwachsinnige Leitung hinter dem Zylinderkopf entfernt werden, wer braucht schon eine Kraftstoff Vorheizung nur für den rechten Vergaser, dann klappt es auch mit dem Leerlauf. Jetzt suche ich noch einen Kraftstoffhahn mit Reservestellung.

Maybe a risk of being lynched for mentioning this on a Norton site, but I've been using genuine Honda fuel hose on various old bikes for years now, it seems the only stuff that really withstands the hardening effect of modern fuel.

My Honda lawn tractor is over 20 years old and has this hose fitted originally, that's where I got the idea of trying it.

I got mine from David Silvers Honda spares , but also probably available from your Local Honda dealer or Honda power equipment shop.

https://www.davidsilverspares.co.uk/tubes/

Not cheap tho...