Problems with water!

Hello, this is my first posting here, so I'm hoping someone may be able to help.

For the last two years, we have been having real problems with a chemical taste in our fresh water. I cleaned the system using Milton, then concentrated orange juice, and more recently have tried the Truma cleaning products all to no avail.  We fitted a water filter, and even changed the aquaroll, but the taste still comes through.

In desperation, I cut open a section of pipework (the flexible blue 3/8" stuff) in the feed to the tap, and found a sticky almost tar like deposit in the bottom which smells quite unpleasant, and so have ripped out the feed from the water inlet to the tap, separating it from the rest of the cold water pipework, and I elected to use Whale semi-rigid 12mm pipework and push-fittings for the new piping.

Being under pressure to get it finished today as we were due to go to Blackshaw Moor on Sunday, I connected it all up, checking every joint was pushed firmly into its respective fitting, and then hooked up the aquaroll.  To put it mildly, each of the push-fit connections is leaking like a sieve!  As a result, I pumped about 4 pints of water into the bed locker base before I could switch off the pump, and so have now had to cancel next week's trip away as we try to dry out the 'van.  Clearly I must be doing something wrong with these push-fit fittings (which I understand are almost universally used on new caravans), but followed the instructions about cutting the tubing and assembling the joint (ie push pipe firmly up against the stop), and so am at a loss to know what's wrong.

I am tempted to go out and buy "old fashioned" 3/8" tube, t-pieces, etc and good old jubilee clips and effectively rebuild the old system, but having spent about £20 on pipe and fittings I am a bit reluctant to give up yet.

Am I missing something obvious?

My caravan incidentally is an ageing but in good condition Bailey Ranger 460/2 - apart from now being a bit damp in the bed locker!