D2 SLS and towing help needed

Hi all my disco keeps dropping all its air on both sides some times while driving sometimes after I've just parked, ive fitted new bumpstops on the rear (the old ones were just tin plates) and new hight sensors, just got a job lot on flea bay compressor, air bags, hight sensors, and slab thingy. So my first question is how do I release all the air out of the system manually to change the parts?

I bought a twin axle caravan weighing in at 1600kg but my disco feels so sluggish like its struggling to tow it, and when I reversed it into my dads it struggled and felt like I was trying to push a pallet of bricks, the caravan it's all checked out and in perfect running order so I know it's not the van that's causing it. So my second question is what could be wrong with my disco?

Thanks in advance for any replys

Ask in the disco section below

https://www.landyzone.co.uk/forum/land-rover-discovery.8/