Hypo scrub rinse then Hypo again scrub rinse .
Try thick bleach boosted with hypo this may cling to glass for longer contact

Here's one

You always get more info off USA sites - so you get 20% chemical - if my maths are correct you would use 2.1 litres of Hypo a min
which would give you 1.4% strength


Max Pressure: 5500 PSI
Max Temperature: 190°F
Up to a 10% injection draw rate
Made in the USA
Orifice: 2.2 mm
Flow Rate: 3.0 to 5.0 GPM
Inlet: 3/8" NPT-M
Outlet: 3/8" NPT-M
Hose barb: 1/4"
Materials: Stainless Steel
Weight: 0.25 lbs.



Or this - you can buy them to mix from 1% to 5%
already has a qr to fit on the lance and another qr for the nozzle

Stainless Injector with couplings (Blue, Red or Clear pipe)
High quality stainless steel foam injector including stainless steel quick couplings. Dosage orrifice plate at required % with pick up tube and strainer.
(Different orrifice percentages at 1% to 5%)

OP - your not really listening - as Stoots said your itching to blow 4k regardless

Splash has already said 21 lpm is enough and he does a fair bit of work - I've never needed more than this either maybe if you get a contract on the rigs or something....

You can get a great set up for around 2k - and thats if you really want to have a fsc as well - I only use them on tarmac and concrete
which is about 5% of work that comes in.

You could spend that 4k and the machine sit there week in and week out - that monies gone where as 2k leaves you 2k for leaflets - advert - web page should you need it

Any idea what it is ?

are there a lot trees around it ?

Hypo would be my next go to - unless its like a tree sap or you might want to use a large non scratch pad on a holder - bit like bronze wool

Just the one side needs cleaning. I had a go at it today and failed miserably. I sprayed it with Virosol and it didn't touch it. It doesn't matter if chemicals are used as the drain off is to the ground.

Hypo mix , smaller brush so you can apply more pressure and hot water