just pour it in!
are you talking about forecourt biodiesel, or veg oil?
if its veg, then a mk1 will run very happily on a 50/50 mix, a bit more in summer, a bit less in winter.
you will find that your fuel filter will clog very quickly initialy, as the oil dislodges all the crud from the fuel system, so a few regular changes will be needed, and possibly water draining will be required from the filter too.
have been using it for about 3 yrs now, in 2 different mk1's. no problems.
