Hydraulic hose flare nut wrench
This tool is specifically made to release and tighten compression nuts on hydraulic hoses.
It will keep the nut in good shape. Normally wrench number 9 (Metric) will fit on most of the hoses apart from the hose running from the high presure pump to the regulator. If possible try to get a wrench with a six side head as shown on the picture. FACOM produces a fine example with order number (FACOM 102100). Since 9 is not commonly used it's rather hard to find these. Replacement nuts ususally can be handled using nr 10.
Hydraulic hose cutting tool
This tool can be used to cut hydraulic hose. It leaves a smooth cut. Try to a buy a small one so you can make cuts in very narrow spaces (if neccesary). Also select one which is suitable for the small hose diameter used on the ID/DS (> 3mm).
Hydraulic hose bending tool
This tool can bend a hose if you want to make your own to replace an old hose. Hose can be bought per meter, most ID/DS specialists have the hose available. When purchasing this tool (used normally for bending brake pipes) select the tool to match the hose diameter. Otherwise it will be impossible to make a proper bend.
Hydraulic hose flaring tool
The regular flairing tools used e.g. for brake system can not be used because Citroën used a different flaring technique.
Flaring tools however can be obtained from some ID/DS specialists.
Again try to obtain a small device which enables you to make a new flair while the hose is still on the car.
The purpose of this is to enable you to make repair patches using the original hydraulic hose connectors as used throughout the cars, and a
(short) new piece of hose. This will enable you in most cases to get running again during e.g. a long trip
(things tend not to break down on your door step).
Or make a simple and cheap DIY flairing tool.