Red grapefruit marmalade

In addition to the baking and cooking for tomorrow, I'm making marmalade, I have a little stall at small fairs around the area over the year and I sell my homemade produce, preserves, today I'm making red grapefruit marmalade.
It's a lengthy process but not particularly difficult.

Juice 5 nice big red grapefruits, and 3 lemons.
Put the juice into a large pan with a lid.
Put the pips into a muslin bag or I have a spice infuser that I use, and place in the pan.
Then, with a sharp knife, slice the skins of the fruits into thin strips and chuck in the pan, add 2 pints of water and bring to a boil, turn down to the gentlest of simmers and put on the lid and leave to cook slowly for 2 hours.
Take out muslin bag and cool enough so you can squeeze as much as you can out of it, back into the liquid, then add 3lb sugar, bring to a hard boil and check for setting point. Pot up.
At this point I'm not going into all the ins and outs of jam making, I wash and dry my jars by hand and then sterilise in the oven at 150 for 15 mins, allow to cool slightly for 5 mins before potting up.
makes the most gorgeous rich orange coloured marmalade, really tangy. Today's efforts made 8 and a bit  good sized jars.