Is it possible to add extra sealant around any push fit connectors.

No need. Use the following 'push-fit' product below. Tried & tested, in my opinion the best on the market. I use this product both in installing heating circuits (hidden from view) and plumbing too. Read carefully the manufacturers installation instructions if you are unfamiliar with this type of product! http://www.johnguest.com/speedfit/ Copy and paste into your browser Tip: Use a good quality plastic pipe cutter to achieve a nice neat and clean square cut, such as the one below: http://www.dartsystems.co.uk/products/plumbing-tools-plastic-pipe-cutters-c-72_202_200/ridgid-20191-model-1442n-ratchet-cutter-p-355.html?zenid=zYkauPptN72sbxibZdKVc1

I'd agree with the previous answer. Don't be spooked by plastic pipe and push fit, they are proven technology these days. Adding a third party sealant into a push fit connector is only going to cause problems. The sealant you introduce could even cause deterioration of the manufacturers seals inside the joint. - Follow the manufactures instructions to the letter! - Don't mix inserts from different manufactures - When making a joint, make a little mark on the pipe with a marker pen about 1" from the end. When you push the pipe into the fitting the mark will reassure you it has gone the complete depth into the fitting. - A good quality pipe cutter gives perpendicular, clean, burr free cuts which prevent potential malfunction of the internal sealing mechanism of a push fit connector. Do not use a hack saw to cut pipe! - Use the manufactures locking clips for extra peace of mind. - Plastic pipe is flexible but don't force it. Stressed joints are not good, pipe work should sit naturally and be supported with clips; just the same as in copper.