Gregg Wallace explores the Manchester factory that produces 700,000 toilet rolls a day. He begins 940 miles away in Sweden, where the raw material - wood - is harvested from a sustainable forest of one billion spruce trees. Most of the wood is used for timber, but the offcuts are turned into sheets of wood pulp. Gregg follows this pulp to Manchester, where he learns that two types of wood fibre - long and short - are required for a loo roll, to give it strength but also softness. He watches as 3,750 kilos of fibre are combined with 34,000 litres of water and sprayed into a 40-metre-long, 11-metre-high paper-making machine. It takes just four seconds for the watery pulp mix to be transformed into soft, dry paper. It is then rolled onto a 1.2 tonne supersized toilet roll known as a 'mother reel'. Each one of these gives birth to 25,000 individual toilet rolls.

Meanwhile, Cherry Healey is at Britain's oldest toilet factory, where they churn out 1,000 loos a day. And she gets the bum deal of following the flush through the sewers and water treatment works of Brighton, finding out how sewage is cleared of debris, grease and bacteria, and transformed into clean water in a little over an hour after flushing. She has a cheeky encounter with a high-tech Japanese toilet and heads to Cranfield University to see a prototype toilet that does away with the need for water altogether. Could this be the toilet of the future that gives one-third of the world's population access to efficient sanitation?

Historian Ruth Goodman finds out what was used to wipe with before the invention of toilet paper. She discovers that the weapon of choice in the American midwest was a dried-out corn cob. And that it wasn't until the 1930s that toilet paper was guaranteed 'splinter free'. She is also in myth-busting mode, finally laying to rest the idea that Thomas Crapper invented the modern toilet. She heads into the House of Lords to check out an 18th-century flushing toilet, still in use today, and discovers that the Great Stink of 1858 expedited a period of sanitary invention that led to the toilet we know today.

Gregg Wallace explores the Nottinghamshire factory that produces 250,000 jars of curry sauce each day. Gregg is making a supersized 3,000-kilo batch of tikka masala - enough to feed 25,000 people. He loads in almost half a tonne of yoghurt and cream and ten other ingredients, including 30 kilos - or 10,000 cloves - of garlic. He deploys an unusual kitchen implement - a hosepipe - to get his ingredients into the cooking pot and heats it for 30 minutes. Then he checks it for colour against a decorating colour chart. Finally his jars head into a pasteuriser for a second two-hour cooking session.

Meanwhile, Cherry Healey is in Guntur, the chilli capital of India, where they sell 3,500 tonnes of chilli each day. She helps to harvest the chillies on a typical small-scale farm, dries and packs them down then follows them through processing into chilli powder. Cherry also gets the lowdown on cooking rice with four foolproof rules which ensure it comes out right every time, and learns how to beat the burn if you have overdone it in the curry house. It turns out that milk is the right choice because the fat dissolves the capsaicin that is responsible for that burning sensation.

Historian Ruth Goodman finds that our passion for curry is around 370 years older than the supposed invention of tikka masala in a Glaswegian restaurant in the 1970s. She recreates a 1747 recipe for rabbit curry, and learns that the word 'curry' itself is a misunderstanding of the Tamil word 'kari'. And she re-examines the early convenience curries of the 1970s and talks to the British Asian housewife whose curry crusade helped to make high street curries closer to Indian home cooking.