How to apply Waxoyl?

I use my compressor and gun to apply it if I'm doing the full underside of a car. If I'm doing small areas or inside a door etc I use a paintbrush. You can actually use a good quality garden sprayer - the type you pump up to pressurise - to ok effect if you thin the waxoyl with white spirit.

Do you mean in the luggage compartment? If so only under bits covered by carpet, otherwise your shopping will get covered in sticky goo...

In the past I have heated the can up in boiling water and used a spraygun (as a young apprentice on the gaffer's Land Rover), but it's pretty easy to splodge it on with a paintbrush if you don't have a compressor.

Umm, don't. Apply waxoyl I mean. Do a little bit of research first into the products available as an alternative. Visit the Bilt Hamber website, or look at Dinitrol stuff. You get what you pay for, and because it is a horrid, messy job, do it properly, and less often.
You get what you pay for with this stuff.

What really? Is Waxoyl really that bad?

I'm surprised because that's what people are telling me to do. Looks like OP and I at least will be learning something!

Brushed on a mix of black and clear waxoyl . Got a nice finish and 99% wasn't on me at all.

Wouldn't like to do it in my back under a car at all.

I warm the waxoil in a bucket of hot water, then apply it with a garden fence/weedkiller sprayer, the type with the hand pump on top, goes on easy and you can change the nozzle (twisting it) from jet to fan spray to do floors and inside chassis ect, if you heat it it solidfys quicker on contact with the vehical and there's less run off and drips, if you thin it with diesel it drips for ages and makes a right old mess of the floor under the car for days.
Ive done litteraly hundred of cars this way, never get in a mess (long nozzle on the sprayer so i stay well away from any drips) mainly cos i don't thin the waxoil i heat it, allways flush the sprayer with diesel or similar or the knozzle will block when the waxoil hardens over time !
There are better products out there but it does work fine if you apply it well (thin and runny) and make sure the vehical is clean and dry, i jet wash then dry with a heater and a hair dryer, i usually wash it then sit it in the garage on stands with the heater blowing under it for a few hours then use the hair dryer to pre warm the chassis rails to get the waxoil to flow into the nooks and crannys before it cools and thickens

I'm sure the stuff itself is ok chemically. My gripe with it is that I have seen it shrink and crack only months later, leaving small unprotected fault lines. You then end up having to apply more on top. So I figure, best to use something that is more flexible.
I also think some people talk about waxoyl as the general product type, like people talk about a Hoover even when it is not the brand.
All of the Bilt Hamber stuff comes in aerosol with a lance extension, so you don't need to worry about other equipment.

I mix it 50/50 with clean 20W/50 engine oil (the cheapest I can get), then stand it in hot water for a good 30 minutes to make sure it is thoroughly warm - then spray using a hand pump.

Adding the oil makes it penetrate better and prevents the cracking mentioned above. Done that way I reckon it's better than some of the expensive branded items. Applied on its own then it isn't nearly as good.

Here's my kit, been using if for around 10 years, cant say i've ever had the shrinking issue myself but then i do slather it on/in ?