yosafa

Hi Everyone, Firstly, I would like to apologise as I am not as knowledgeable in the science field hence me requiring the help of you all. I need to know about the chemical reaction and consequences relative to my query and questions below. Thank you to all in advace for your answers and advice. ____________The outdoor garden drain is blocked quite severely with years of fat, oils, grease build etc.. Most likely from the previous owner of the home, with the addition to my own. The problem started as I noticed my kitchen sink was not allowing water to drain and was coming back up. I change the old trap, u bend and waste pipe. The waste pipe comes out the external garden warn and into the outdoor drain gully grid. I replaced all waste pipes from the sink, all new, but the problem was still happening. I did not notice the water at the time was rising from the outdoor drain until today which then indicated a drain block coming out of the gully grid. I removed the grid and removed a lot of thick fat & grease by hand. Problem/solution/Questions. Even though I have unblocked the drain a little bit, there is a lot of remnants of fat and grease left which has tucked into the grooves of the drain pipes. I have tried going at this with drain rod, and pressure washer jet washes pipe, though it just will not budge. I was thinking of using a chemical such as caustic soda to eat away the fats and eventually block the drain though I worry about using such chemical. My worries are1. Will caustic soda actually do the job of unblocking the drains?2. If I was to pour in the diluted caustic soda, will it eventually harden again elsewhere in my drainage system causing a major block or will it just wash away the cooler it gets from the moist? From reading and guidance, the Caustic soda should be added to cold water as it heats up which then can be poured into the drain according to ratio guidance on the label. Additionally, this chemical is known the harden3. Because the chemical gets hot when reaction with water, will this in turn damage the underground PVCu Drainage pipe or again will it just cool and wash away. I know the PVCu has high heat resistance though, does the chemical pass the PVCu heat threshold which may then cause damage. If all else fails, then could you guys recommend me a possible home remedy or ideas to just unblock the grease and fat leaving it overnight etc... then wash away. Sorry guys for the many questions, though, I hope you can all help me regarding this. I just want to be sure before putting anything in my drains which may do potential harm.Thank you to all who reply in advance and give opinions on the use of caustic soda and whether it worked for you or not. Thanks again.