Note that arteries have muscles that control their diameter. This is the method how "blood pressure and flow" is controlled systemically. Aneurysisms (burst arteries, arterioles - high pressure side of capillaries) are relatively rare.

Note also that the "return of blood" is not primarily due to the "pushing" of old blood by new blood, but by the rhythmic compression and release of veins by adjacent pulsing arteries combined with non return valves in the veins. This is also aided (naturally when required by "pulsing' of normal body musculature when exercising.)

I would suspect that the biggest problem giraffes have (usually only while drinking) is to return "used blood" to allow space for new oxygenated blood. Although the "swallowing" muscles probably aid this process, nevertheless it is not  normally sufficient and that is why giraffes lift their heads up several times during long drinking sprees. (This behaviour is surmise on my part and requires verification.) 

The giraffe has a special structure in the neck, the name of which has slipped my mind, that regulates blood flow and hence blood pressure in the brain.

This is not the only problem that the creature has. Because of the rather large head of blood in the giraffe's system, the giraffe experiences very high pressures in the lower parts of each leg. This is overcome by a very tight sheath of tissue covering the lower part of the legs which acts in much the same way as a fighter pilot's G-suit.

I suggest you watch this >>> http://www.channel4.com/programmes/inside-natures-giants/4od#3072424It's an episode of Channel 4's 'Inside nature's giants' in which they dissect a giraffe and I think they talk about it's circulatory system quite a lot. Hope it helps